The present invention generally relates to extruding a plastic food product, particularly to weaving food extrudates, and specifically to weaving high-speed food extrudates.
Appearance and texture of cereal pieces in addition to the particular food components utilized comprise important factors in the marketing of ready-to-eat cereal. Woven cereal pieces having a braided appearance and in particular including thin, multiple extrudates (e.g. 4 to 8) twisted to form a braid are believed to have particular market acceptance, and are believed to have a beneficial effect on texture and especially in regard to making high fiber products more palatable and extending cereal life when immersed in milk. Such a braid can be formed by extruding the extrudate using a rotating spindle or rotor. However, problems have been encountered in the food industry in providing a seal with the rotating spindle for preventing the escape of the extrudate from the housing around the rotor. In particular, although the plastics industry utilizes rotary dies, the speed of the extrudate is considerably faster in the food industry than in the plastic industry, with the linear speed of the extrudate in the food industry being as much as 10 times faster than in the plastics industry. The faster the extrudate speed, the faster the rotor must rotate to provide the same criss-cross weave pattern.
Conventional mechanical or elastomeric seals can be designed to withstand high speeds or high pressures but not both at the same time. These seals rely on pressure or force to hold the sealing surfaces together. The higher the pressure across the seal, the more force is needed to hold the sealing surfaces together. The combination of high forces and high-speed rotation creates tremendous amounts of friction which wears the seal out quickly.
Thus, a need exists in the food industry for assembly and methods for weaving high-speed food extrudates. In particular, a need exists for a method and assembly for providing a seal between a shaft or rotor rotating at relatively high speeds and subjected to high extrusion pressures and which is not prone to wear or otherwise fail in normal operation.